Abstract:
This work reports the effect of co-sensitization of nanoporous titanium dioxide using
Cadmium Sulfide (CdS) and poly(3-hexylthiophene) (P3HT) on the performance of hybrid solar cells.
CdS nanolayer with different thicknesses was grown on Titanium Dioxide (TiO2) nanoparticles by
chemical bath deposition technique with varying deposition times. Both atomic force microscopy
(AFM) and UV–Vis–NIR spectroscopy measurements of TiO2 electrode sensitized with and without
CdS layer confirm that the existence of CdS layer on TiO2 nanoparticles. AFM images of CdS-coated
TiO2 nanoparticles show that the surface roughness of the TiO2 nanoparticle samples decreases with
increasing CdS deposition times. Current density–voltage and external quantum efficiency (EQE)
measurements were carried out for corresponding solar cells. Both short circuit current density (JSC)
and fill factor were optimized at the CdS deposition time of 12 min. On the other hand, a steady and
continuous increment in the open circuit voltage (VOC) was observed with increasing CdS deposition
time and increased up to 0.81 V when the deposition time was 24 min. This may be attributed to the
increased gradual separation of P3HT and TiO2 phases and their isolation at the interfaces. The higher
VOC of 0.81 V was due to the higher built-in voltage at the CdS–P3HT interface when compared
to that at the TiO2–P3HT interface. Optimized nanoporous TiO2 solar cells with CdS and P3HT
co-sensitizers showed external quantum efficiency (EQE) of over 40% and 80% at the wavelengths
corresponding to strong absorption of the polymer and CdS, respectively. The cells showed an overall
average efficiency of over 2.4% under the illumination of 70 mW/cm2 at AM 1.5 condition.
